Statistics, Morphology, and Energetics of Ellerman Bombs
We investigate the statistical properties of Ellerman bombs in the dynamic emerging flux region NOAA 8844, underneath an expanding arch filament system. High-resolution chromospheric Hα filtergrams (spatial resolution 0.8 ), as well as photospheric vector magnetograms (spatial resolution 0.5 ), and Dopplergrams, have been acquired by the balloon-borne Flare Genesis Experiment. Hα observations reveal the first "seeing-free" data set on Ellerman bombs and one of the largest samples of these
... ples of these events. We find that Ellerman bombs occur and recur in preferential locations in the low chromosphere, either above, or in the absence of, photospheric neutral magnetic lines. Ellerman bombs are associated with photospheric downflows and their loci follow the transverse mass flows on the photosphere. They are small-scale events, with typical size 1.8 × 1.1 arcsec 2 , but this size depends on the instrumental resolution. A large number of Ellerman bombs are probably undetected, due to limited spatial resolution. Ellerman bombs occur in clusters which exhibit fractal properties. The fractal dimension, with an average value ∼ 1.4, does not change significantly in the course of time. Typical parameters of Ellerman bombs are interrelated and obey power-law distribution functions, as in case of flaring and sub-flaring activity. We find that Ellerman bombs may occur on separatrix, or quasi-separatrix, layers, in the low chromosphere. A plausible triggering mechanism of Ellerman bombs is stochastic magnetic reconnection caused by the turbulent evolution of the low-lying magnetic fields and the continuous re-shaping of separatrix layers. The total energies of Ellerman bombs are estimated in the range (10 27 , 10 28 ) erg, the temperature enhancement in the radiating volume is ∼ 2×10 3 K and the timescale of radiative cooling is short, of the order of a few seconds. The distribution function of the energies of Ellerman bombs exhibits a power-law shape with an index ∼ −2.1. This suggests that Ellerman bombs may contribute significantly to the heating of the low chromosphere in emerging flux regions.